Light emitting devices, such as light emitting diodes or laser diodes, using Group III-V or II-VI compound semiconductor materials may produce various colors such as red, green, and blue, and ultraviolet, thanks to development of thin film growth technologies and device materials. In addition, these light emitting devices may produce white light having high efficiency using fluorescent materials or through color mixing and have advantages, such as low power consumption, semi-permanent lifespan, rapid response time, safety, and environmental friendliness, as compared to conventional light sources, such as fluorescent lamps and incandescent lamps.
Therefore, these light emitting devices are increasingly applied to transmission modules of optical communication units, light emitting diode backlight units substituting for cold cathode fluorescence lamps (CCFLs) constituting backlight units of liquid crystal display (LCD) devices, lighting apparatuses using white light emitting diodes substituting for fluorescent lamps or incandescent lamps, headlights for vehicles, and traffic lights.
The light emitting devices emit light having energy determined by the intrinsic energy band of a material of an active layer through combination of electrons injected through a first conductivity-type semiconductor layer and holes injected through a second conductivity-type semiconductor layer. In a light emitting device package, phosphors are excited by light emitted from a light emitting device, and thus, light of a longer wavelength region than light emitted from an active layer may be emitted.
FIG. 1 is a view illustrating a conventional light emitting device 100. FIG. 2 is a view illustrating an electrode structure of the light emitting device 100 of FIG. 1.
Referring to FIG. 1, the light emitting device 100 includes a substrate 110, a buffer layer 115, and a light emitting structure 120 including a first conductive-type semiconductor layer 122, an active layer 124, and a second conductive-type semiconductor layer 126. Here, the buffer layer 115 is interposed between the substrate 110 and the light emitting structure 120.
When the substrate 110 is formed of a non-conductive material, a portion of the first conductive-type semiconductor layer 122 is exposed and a first electrode 150 is disposed on the exposed surface thereof. To uniformly inject holes into the second conductive-type semiconductor layer 126, a light-transmissive conductive layer 130 may be disposed on the second conductive-type semiconductor layer 126, and a second electrode 160 may be disposed on the light-transmissive conductive layer 130.
FIG. 2 illustrates a structure of the first and second electrodes 150 and 160 of the light emitting device 100 of FIG. 1. To uniformly inject electrons and holes into the respective first and second conductive-type semiconductor layers 122 and 126 and to increase the rate of recombination of electrons and holes, as illustrated in FIG. 2, the first electrode 150 includes a first electrode pad 152 and a first branch electrode 154 branching therefrom, and the second electrode 160 includes a second electrode pad 162 and a second branch electrode 164 branching therefrom.
However, conventional light emitting devices have problems as stated below.
Even though the above-described second branch electrode 165 is disposed on the second conductive-type semiconductor layer 126, holes can be concentrated only around a region of the second conductive-type semiconductor layer 126 which corresponds to the second branch electrode 165, and thus, it is difficult to expect binding of electrons and holes in the entire area of the active layer 124.
To address these problems, the light-transmissive conductive layer 130 having a high ability to disperse holes may be disposed on the second conductive-type semiconductor layer 126. However, since the light-transmissive conductive layer 130 has poor contact characteristics with electrode materials, the second electrode 160 and the second branch electrode 165 may not be stably formed.